3. Simple multi-rotor model

A simple but realistic example, modeled by equations that are easy to solve by hand, is used to highlight the basic phenomena in the dynamic behavior of coaxial multirotors. The chosen method is Rayleigh-Ritz, and two types of multirotor are studied: the first is symmetrical, the second is asymmetrical, since the behavior of symmetrical and asymmetrical rotors is, here too, different. The basic phenomena presented are :

• natural frequencies as a function of speed, Campbell diagram ;

• the effect of the unbalance excitation force.